Relay with contacts of mercury metal composition



G. MERKL Nov. 25, 1969 RELAY WITH CONTACTS OF MERCURY METAL COMPOSITION Filed July 24, 1967 2 Sheets-Sheet l GEOEGE MEEKL MAN 51'.

ATTORNEY Nov. 25, 1969 G. MERKL 3,480,891

RELAY WITH CONTACTS 0F MERCURY METAL COMPOSITION Filed July 24, 1967 2 Sheets-Sheet 2 THERMIS'FOR LIGH N NG TEE.

A-C. all D.c.

IN PUT INVENT OR GEORGE MEI? m.

,, ATTORNEY United States Patent 3,480,891 RELAY WITH CONTACTS OF MERCURY METAL COMPOSITION George Merkl, 517 Boulevard, New Milford, NJ. 07646 Filed July 24, 1967, Ser. No. 655,514 Int. Cl. H01h 29/00 US. Cl. 335-52 3 Claims ABSTRACT OF THE DISCLOSURE A photoelectric street lighting control unit including a thermistor thermally coupled to the photocell for retarding the-response of the control unit to rapid fluctuations in level of the ambient illumination. A relay with stationary contacts formed of a meltable mercury-metal composition is disclosed.

The present invention relates to a photoelectric control for street lighting and more particularly to a control of this type wherein heat derived from the photocell is utilized to heat a thermistor connected in series therewith. The control will not operate to turn off the street light until the termistor has attained a sufficiently high temperature to permit the flow of full operating current through the shut-01f relay winding.

The relay has stationary contacts in theform of a mercury-metal composition which is of pasty consistency when there is no current flow therethrough. When the street light is on, current flow melts the mercury-metal composition so that it liquefies and provides a mercury contact which requires no contact pressure.

The invention is described in greater detail in the following specification with reference to the accompanying drawing forming a part thereof:

In the drawing:

FIGURE 1 is a fragmentary side elevational view showing the upper portion of a street lighting post with a control embodying the invention mounted at its top.

FIGURE 2 is an enlarged view in sectional elevation taken on the line 22 of FIG. 1.

FIGURE 3 is an exploded perspective view of the control shown in FIG. 2.

FIGURE 4 is a circuit diagram including an enlarged view in sectional elevation of the shut-off relay.

Referring to FIG. 1, a lamp post supports a bracket 11 holding street signs 12 and 13. A lighting control unit designated generally as 15 is removably mounted at the top of the lamp post 10. Extending horizontally from the top of the lamp post 10 is an arm 16 the outer end portion 17 of which is downwardly inclined. At the free end of arm 16 there is a street lighting lamp assembly 18 which is photoelectrically controlled by the unit 15.

The control unit 15 comprises a weatherproof cover member 20. The cover member 20 is preferably formed of transparent plastic interiorly coated with a layer 21 of opaque material arranged to leave a transparent window area at 22. The cover member 20 is supported by a circular base member 24. The cover member 20 comprises a lower integrally formed flange portion 25 and a skirt portion 26 which extends downwardly from the periphery of flange portion 25. The upper end of lamp post 10 is dimensioned to fit the skirt portion 26 of cover member 20.

The base 24 comprises a connector plug portion 28 equipped with three twist-lock type prongs 29, 30 and 31. The prongs 29, 30 and 3-1 cooperate with a receptacle (not shown) at the top of the post 10 to connect the control unit 15 to its associated external circuitry and to hold it securely positioned at the top of the post 10. The receptacle is so oriented that, when the unit 15 is in 3,480,891 Patented Nov. 25, 1969 operating position, an arrow 33 above the window area 22 will point toward the north. In the northern hemisphere, direct sunlight will not ordinarily pass through the window area 22.

Within the cover member 20 there is a photocell unit 34. The photocell unit 34 is secured by bolts 35 and 36 to an upright bracket 38 fixed to the upper side of the base member 24. The bolts '35 and 36 also serve as electrical terminals and they are suitably insulated if the bracket 38 is formed of metal.

Centrally located within the cover member 20 directly above the plug portion 28 of base 24 is a relay designated generally as 40.

The relay 40 comprises a circular base member 41 and a hollow cylindrical sleeve member 42 which extends upwardly from the base member 41. Also extending upwardly from the base member 41 is a stationary contact unit 44 which is laterally enclosed by the sleeve member 42. A solenoid operating winding 45 is mounted on top of the contact unit 44 within the sleeve member 42. The winding 45 is provided with diametrically opposed terminals 46 which protrude through open-ended slots 48 outwardly beyond the sleeve member 42.

The contact unit 44 has a chamber 49 formed therein which is closed at its top by the bottom of the solenoid winding 45. The bottom of chamber 49 communicates through vertical cylindrical passages 50 and 51 with stationary contact elements 52 and 53, respectively.

A movable contact member designated generally as 55 comprises an upright cylindrical plunger portion 56, a flange portion 57 and two downwardly extending contact fingers 58 and 59. The movable contact member 55 is shown as an integrally formed member made of steel or iron so that the plunger portion 56 will be drawn upwardly into the solenoid winding 45 upon appropriate energization of terminals 46. When the winding 45 is deenergized, contact fingers 58 and 59 extend through passages 50 and 51 into circuit closing contact with stationary contact elements 52 and 53, respectively.

Although contact elements 52 and 53 could be constituted by pools of mercury, it is preferred to utilize a nonliquid mercury-metallic composition which has a puttylike consistency and which will not spill out through the passages 50 and 51. Moreover, the contact fingers 58 and 59 can penetrate into the mercury-metallic material and establish good electrical constact substantially independently of the magnitude of the contact pressure. The preferred mercury-metallic composition consists essentially of 5- 25% (preferably 10%) Hg; 120% (preferably 10%) Cd; 3-10% (preferably 5%) Cu; and balance Al. This composition is disclosed in greater detail in my copending application Ser. No. 631,349 filed Apr. 17, 1967.

Referring to FIG. 4, two power supply conductors 61 and 62 are shown connected to a lightning arrester 63. Conductors 61 and 62 are also Connected to the control unit 15 through plug terminals 30 and 31. Conductor 61 extends directly to one terminal of the street lamp or load 18. The other terminal of lamp 18 is controlled by relay 40 through plug terminal or prong 2.9.

The photocell unit 34 comprises a photoelectric element 65 in heat transmitting proximity to a thermistor 66. As shown, daylight conditions prevail and current flow through the photoelectric element 65 and thermistor 66 is suflicient to energize the solenoid winding 45 to retain movable contact member 55 held in its uppermost position. Contact fingers 58 and 59 are held withdrawn from stationary contact elements 52 and 53 thereby opening the energizing circuit for street lamp 18.

As evening approaches, the current flow through photoelectric element 65 decreases and its heating effect on thermistor 66 decreases. The resistance of thermistor 66 increases because of the reduced heating and, ultimately,

the current flow through solenoid Winding 45 decreases to a value which is sufficiently low so that the movable contact member 55 drops by gravity and contact fingers 58 and 59 close a circuit between stationary contact elements 52 and 53 which passes through the integrally formed flange portion 57 of movable contact member 5-5. This turns on the street light 18.

If, during the night, there should be a sudden illumination, such as a flash of lightning, the resistance of photocell element 65 will be momentarily reduced. However, thermistor 66 will remain cold and its resistance will be sufficiently high to prevent a momentary interruption of the energizing circuit for street lamp 18 by lifting movable contact member 55.

As daylight approaches, the resistance of photocell element 65 slowly decreases and the increased current flow heats thermistor 66 thereby decreasing its resistance. Gradually, the current flow increases to a magnitude which 1. A relay comprising,vin combination; a base structure;

at least one stationary contact element formed of a mercury-metallic composition of putty-like consistency, said contact element being confined within said base structure; means defining a vertically extending passage in said base structure communicating with said contact element; a movable contact member including a contact finger longitudinally displaceable in said passage for selectively engaging and disengaging said stationary contact element; and electromagnetic means for displacing said movable contact member, said mercury-metallic composition consisting essentially of 525% Hg; 10-20% Cd; 33-10% Cu; and the balance Al.

2. A relay according to claim 1, wherein there are two of said stationary contact elements in laterally spaced relationship, in which said passage defining means defines two separate vertically extending passages each communicating with one of said contact elements; and wherein said movable contact member is formed of electromagnetic material and comprises two of said contact fingers each longitudinally displaceable in one of said passages, said fingers being integrally formed with said movable contact member.

3. A relay according to claim 2, wherein said movable contact member is formed substantially entirely of iron.

References Cited UNITED STATES PATENTS 1,648,100 11/1927 Aichele. 3,133,998 5/1'964 Horowitz 335-52 3,161,745 12/1964 Anderson 335-57 1. D. TRAMMELL, Primary Examiner W. J. SMITH, Assistant Examiner US. Cl. X.R. 200-452; 252512 

